ACT® Science

Most Likely Concentrations

ACTSCI-8RJQPJ

A student is conducting experiments to look at what factors affect the rate of a chemical reaction. The student is measuring the change in iodine $(I_2)$ concentration as the reaction below takes place:

$$ H_2O_2 + 2I^- + H^+ \longrightarrow I_2 + H_2O $$

The student has set up a spectrophotometer to measure the concentration of iodine as the reaction proceeds. The student runs trials to see how changing the concentration of each reactant changes the reaction, and how changing the temperature changes the reaction.

Study 1

The student varies the concentration of one reactant at a time while holding the other reactants constant, then measures the rate of each reaction.

Study 2

The student holds the concentration of the reactants steady and changes the temperatures at which the reactions happen, and records the rate of each reaction.

If the temperature used in study 1 was 340 °C, what would be the MOST likely concentrations for the experiments in study 2?